The present invention relates to a process for forming high temperature oxide superconductors of Y-Ba-Cu-O, Bi-Ca-Sr-Cu-O, Tl-Ca-Ba-Cu-O types.
In conventional processes, high temperature oxide superconductors are prepared by conventional solid state reaction. That is, the metal oxides or/and carbonates desired in the final formula of oxide superconductor are mixed in an appropriate ratio, ground, calcined, and sintered to obtain oxide superconducting materials. The final product obtained in this process gives coarse particulate and poor uniformity in sizes which seriously affects its superconducting property and subsequent application.
The drawbacks of the above process can be improved by employing a method of co-precipitation in which more uniform and finer particulates of superconductive oxide materials can be obtained. However, in this process, the stoichiometry of the coprecipitates is rather difficult to be controlled owing to the different solubility between various ions, and therefore, this process is inappropriate to be used in mass production.
Another method for the production of oxide superconductor is by employing a citrate gel as a precursor. The precursor is calcined and sintered to form a powdery form of superconductive oxide materials. In this method, the ratios of the individual metal components can be easily controlled as compared to the coprecipitation method, and thus this method can suitably be used in mass production of superconductive oxide materials. However, there are still drawbacks in this method. For instance, the citrate gel of an alkaline earth cannot be easily formed in acid solution and the interaction within them is poor.